This invention relates to a process for sensing the quality of the coupling between the therapy head of an extracorporal shock wave lithotritor and the body of the patient being treated.
In extracorporal shock wave lithotrity (ESWL), the patient's body is coupled to the therapy head of the shock wave therapy unit by means of a water cushion. When the coupling is insufficient, shock waves are reflected back into the therapy head on water-air transition areas, which can result in damage to the in-line sonic head of an ultrasonic locating device arranged in the therapy head. In addition, when the coupling is insufficient, the effectiveness of the therapy is substantially impaired, which represents avoidable stress to the patient.
German Patent Document DE 39 13 023 A1 discloses a crushing-wave treatment unit in which an ultrasonic image transducer is integrated into the crushing-wave therapy head. From ultrasonic images taken before and during the application of the crushing waves, subtraction images are generated in order to monitor the condition of the concrement to be destroyed.
In German Patent Document DE 39 00 893 A1, a shock wave treatment unit is disclosed in which the generation of a shock wave is prevented when the overlap between the object to be destroyed and the focal point of the shock wave therapy head is too small. For this purpose, overlap of the object to be destroyed, shown in an ultrasonic image and a focal-point zone marking brought into the ultrasonic image, is determined.
It is an object of the present invention to provide a process by means of which the quality of the coupling can be detected.
This object is achieved by the process according to the invention in which the sonic head of an ultrasonic locating device is integrated as an in-line sonic head in the therapy head of the lithotritor, and at least one ultrasonic image is taken when the patient's body is coupled. This ultrasonic image is then compared with an ultrasonic image which was taken when the patient's body was not coupled (that is, a "blank image" or "uncoupled image"). For this purpose, the comparison is based on those repeating echoes which are characteristic of an insufficient or non-existing coupling, and which are absent in the case of a proper coupling.
In the case of a defective coupling, warning signals may be generated, and the shock wave therapy unit may be automatically switched off, thus preventing reflection of the shock wave and unnecessary stress to the patient. Also, the life of the shock wave therapy and the integrated ultrasonic head are extended considerably.
Generation of shock waves in the therapy head may take place by means of known methods (including electromagnetic, piezoceramic and electrohydraulic processes).
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.